Magnetic domain propagation arrangement

ABSTRACT

A single electrical conductor to which an AC signal is applied causes movement of a single wall domain therealong in a substrate of magnetic material in which such domains can be moved.

United States Patent Inventor John Alexander Copeland, III

Gillette, NJ.

Appl. No. 49,272

Filed June 24, 1970 Patented Dec. 28, 1971 Assignee Bell Telephone Laboratories, Incorporated Murray Hill, NJ.

MAGNETIC DOMAIN PROPAGATION Primary Examiner-Daryl W. Cook Attorneys-R. J. Guenther and Kenneth B. Hamlin ARRANGEMENT 8 Claims, 6 Drawing Figs.

US. Cl. ..340/174 MC ABSTRACT: A single electrical conductor to which an AC InLCl. Gllb 5/62 signal is applied causes movement of a single wall domain Field of Search 340/174 therealong in a substrate of magnetic material in which such LC, 174 MC, 174 TF, 174 SR domains can be moved.

CONTROL R IT CU ems FIELD AC E SOURCE SOURC 23 25 I l: :3 I 8 3 g a E I z i U I l 9 I I I LE 1 I D I I I J z F L 3 Patented Dec. 28, 1971 3,631,413

F/G.l

6 CONTROL CIRCUIT BIAS FIELD AC 7 SOURCE SOURCE I l6 I4 23 25 2% I I 5 I E E I U 6 I g i I l I, Q I a I II. l I. I E I 3 F/G.ZB

lNI/ENTOR J. A COPELAND 1Z1 ATTORNEY MAGNETIC DOMAIN PROPAGATION ARRANGEMENT FIELD OF THE INVENTION This invention relates to data processing arrangements and, more particularly, to such arrangements including a material in which single wall domains can be moved.

BACKGROUND OF THE INVENTION A single wall domain is a magnetic domain encompassed, in the plane of a material in which it can be moved, by a domain wall which closes on itself to form a stable entity free to move in the plane. A typical material for such an arrangement is a rare earth orthoferrite or a garnet crystal having a preferred direction of magnetization along an axis out of the plane of movement, nominally normal to the plane. It is convenient to designate one direction along that axis (viz., the positive direction) as the direction of the magnetization of the domain, the remainder of the material having its magnetization in the negative direction. Such a convention permits a domain to be represented as an encircled plus sign in a field of negative signs or, more simply, as a circle. A single wall domain and an arrangement for manipulating such domains are disclosed in U.S. Pat. No. 3,460,116 of A. H. Bobeck, U. P. Gianola, R. C. Sherwood, and W. Shockley, issued Aug. 5, 1969.

Single wall domains in a sheet of material are constrained to a given diameter typically by a bias field of a polarity to constrict domains a negative polarity according to the assumed convention. Domains are moved in the sheet by a field (viz, a field gradient) which is provided in positions consecutively offset from the position occupied by a domain.

Field gradients for moving domains are provided generally by pulses applied to an array of conductor loops adjacent the surface of the material in which the domains are moved. By pulsing a succession of conductors consecutively ofiset from the position occupied by a domain, consecutively offset gradients are established for causing domain displacement. In practice, the conductors are interconnected serially in three sets to provide a familiar three-phase shift register operation for domain patterns. A propagation arrangement of this type is disclosed also in US. Pat. No. 3,460,l [6, supra.

It has been difficult to achieve conductor arrays with geometries suitable for the movement of minute domains. In order to generate fields suitable for moving domains, minimum currents must flow in the conductors of the array. This current-carrying requirement imposes a minimum crosssectional area on each conductor. For achieving a suitable cross section, thin conductors are formed by photolithographic techniques and plated, thereafter, to a suitable thickness. The plating process widens the conductors, as well, causing short circuits which are difficult to avoid when the array is dimensioned for moving domains having diameters on the order of microns (viz, 2 .1.). If the conductors are spaced further apart to avoid short circuits, packing density is sacrificed.

A simplification of the conductor geometry leads to an acceptable conductor spacing without sacrificing packing density. Such a circuit was the objective of US. Pat. No. 3,506,975 of A. H. Bobeck and R. F. Fischer, issued Apr. 14, I970. The conductors in the circuit of that patent are generally zigzag in geometry, and are pulsed consecutively for moving domains along channels each defined by a plurality of the conductors. with such circuits, suitably thick conductors are achieved without sacrificing packing density.

A domain channel which is defined by a plurality of electrical conductors, on the other hand, is subject to a number of practical constraints. A most important constraint is the fact that certain types of channel geometries as, for example, a closed loop geometry for recirculating information are achieved either by having conductors cross over one another or by a relatively complicated geometry in which a conductor requires a mirror image return path for generating the requisite fields. The former requires a three-dimensional conductor array which is relatively costly. The latter necessitates a redundant wiring arrangement which is wasteful of space in that domain interactions are such as to permit adjacent channels to be more closely spaced than such a redundant wiring pattern permits. Moreover, the latter also necessitates an increase in the length of the conductors at each bit location attended by an increased line resistance and, thus, voltage.

BRIEF DESCRIPTION OF THE INVENTION In accordance with this invention, a single electrical conductor defines a domain propagation channel. Specifically, a single wall domain is displaced in a slice of a suitable magnetic material along an axis defined by a single electrical conductor folded back and forth on itself to form a chevron-type pattern. An AC current signal applied to the conductor alternates the geometry of the domain between a sausage and a circular shape (in cross section). The change in geometry is accompanied by a displacement of the center of geometry along the axis of the conductor because of a nonzero coercive force characteristic of the slice in which the domains move. The displacement is in the direction of the closest low-energy region which appears when the current in the conductor reverses.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of a domain propagation arrangement in accordance with this invention;

FIGS. 2A, 2B, 2C, and 2D are schematic illustrations of a portion of the arrangement of FIG. 1 showing consecutive magnetic conditions therein during operation; and

FIG. 3 is a pulse diagram for the arrangement of FIG. 1 for achieving domain displacement.

DETAILED-DESCRIPTION FIG. 1 shows a domain propagation arrangement in accordance with this invention. The arrangement comprises a slice 11 of material in which single wall domains can be moved. A plurality of domain propagation channels are defined in slice 11 by chevron-shaped electrical conductors shown in detail by a conductor 12 aligned along an axis 13 between input and output positions I and 0 respectively. Conductor 12 is connected between AC signal source 14 and ground.

The geometry of conductor 12 is chosen such that the shape of domains moving along channel 13 is altered when an AC signal is applied to the conductor. Such an alteration is illustrated in FIGS. 2A, 2B, 2C, and 2D where a domain D is shown in representative consecutive positions in channel 13. The nominal diameter of domain D is maintained by a bias field of a polarity to constrict domains generated by familiar means represented by block 16 of FIG. 1.

A graph showing an illustrative current signal I (versus time T) is shown in FIG. 3. It is assumed that positive currents generate fields which attract domains into loops of the conductor where the current is flowing counterclockwise. A positive current is in the direction indicated by arrow i in FIG. 2A. The fields generated by the current are' positive and negative as indicated by the signs in FIG. 2A. A domain D, in'a position shown by the broken circle in FIG. 2A when a positive current is applied to conductor 12, is displaced to the right to the position designatedm'lhe corresponding positive current pulse in conductor 12 as shown in FIG. 3 is also designated.lhe domain encounters an attracting field which enlarges the domain to conform to the shape of the conductors-a sausage shape. When the current signal in conductor 12 goes to zero as indicated atin FIG. 3, domain D assumes its nominal circular geometry under the influence of the bias field and the change in shape results in a displacement of the domain wall (and thus the center of geometry) to the right because of a nonzero coercive force of the material of sheet 11. The centers of geometry for a circular domain at the assumed starting position and for the sausage-shaped domain are designated 17 and 18 in FIG. 2A.

The resulting position and geometry of the domain under these conditions are illustrated atin FIG. 2B. The center of the geometry is designated 19.

The next subsequent signal in conductor 12 is negative as indicated atin FIG. 3. Domain D again moves to the right and conforms to the geometry of the conductor as illustrated atQin FIG. 2C. When the current again goes to zero, domain D again assumes its circular shape as shown in FIG. 2, and again the center of geometry is displaced to the right.

The distortion of a circular domain is exaggerated in the figures. Actually, little distortion is necessary for propagation and the amount of distortion depends on the magnitude of the bias field.

It is important to note that the size of the domain and the geometry of conductor 12 bear a relationship to one another such that the domain overlaps the conductor as shown at(Z)in FIG. 28. Not only does this ensure that an attracting field is operative on at least a portion of the domain but imposes on the domain distortion on asymmetry which results in displacement rather than oscillation.

On the other hand, a symmetric conductor pattern may be used if, for example, permalloy dots or recesses in sheet 11 of FIG. 1 are employed to offset the domains during each alternation as shown in copending application Ser. No. 813,475, filed Apr. 4, 1969 for R. F. Fischer, now U.S. Pat. No. 3,564,518 Such a symmetrical circuit with permalloy dots (or recessions), illustratively having twice the spatial periodicity of the conductor, is illustrated at channel in FIG. 1. Domain D is offset, in such a symmetric arrangement, to the position shown in FIG. 1 when the drive field goes to zero (Q of FIG.'3).

Domain movement in accordance with this invention has been illustrated in terms of a representative domain. It should be clear, however, that the repetitive geometry of conductor 12 permits the simultaneous movement of domain patterns.

Domain patterns for movement in this manner are generated at an input position I in FIG. 1 and detected at an output position 0. One familiar input arrangement for generating domain patterns includes a conductor which separates a domain (viz, binary one) from a source region of positive magnetization, in accordance with the assumed convention, when pulsed. Such an arrangement is shown in U.S. Pat. No. 3,460,l l6, supra. The absence of a pulse on the conductor results in the absence of a domain (viz, binary zero) for propagation. The input arrangement is represented by an arrow 22 originating from a block 23 entitled Input Circuit.

Detection of domains, so generated and propagated, is achieved by any one of a variety of electrical or optical means such as via a Hall probe or by the Faraday effect. Such a means is represented by an encircled X sign in FIG. 1 along with an arrow 24 to a utilization circuit represented by block 25. One suitable detection arrangement is disclosed in copending application, Ser. No. 882,900, filed Dec. 8, 1969 for W. Strauss.

Sources 14 and I6 and circuits 23 and 25 are connected to a control circuit 26 for activation and synchronization. The various sources and circuits may be any such elements capable of operating in accordance with this invention. 1

The displacement of the center of geometry of domain D from 18 of FIG. 2A to 19 of FIG. 2B is due to the nonzero coercive force of slice ll of FIG. 1. The mechanism involved may be understood as follows: When the current signal in conductor 12 of FIG. 1 is at zero as indicated atQin FIG. 3, the magnetostatic energy of the system is operative on the wall of D atin FIG. 2A. The geometry of conductor 12 is such as to impose an asymmetric distortion of the domain along the axis the low-energy condition for the domain. The magnetostatic energy acts to drive the wall to a least energy condition thus correcting the sharp indentation. The nonzero coercive force of the slice acts to prevent the bulk of the wall m the low energy condition condition from moving.

An arrangement of the type shown in FIG. 1 has been operated for moving domains having a nominal diameter of 125 pm. in a slice of thulium orthoferrite 5 mm. X 5 mm. X 50 pm. thick having a coercive force of a./m. (l oersted). A bias field of 1,600 a./m. was employed. Conductor 12 had a center angle of a period of 200 um. and a width of 500 um. The (copper) conductors were 50 pm. wide and 8 pun. thick. Current pulses of ma. and 300 psec. duration were applied with a frequency of 2 Hz. Bit rates of 1 MHz and packing densities of over l50,000 per inch can be achieved with single conductor configurations of the type described for thulium orthoferrite.

A symmetric conductor arrangement requires dots or recesses of about 30 um. diameter for moving pm. diameter domains in a similar arrangement. The recesses are cone shaped and about 10 um. deep whereas the permalloy dots are about 0.1 pm. thick.

What has been described is considered only illustrative of the principles of this invention. Therefore, various modifications thereof can be devised by those skilled in the art in accordance with those principles within the spirit and scope of this invention.

What is claimed is:

l. A magnetic domain propagation circuit comprising a slice of material in which single wall domains can be moved, an electrical conductor adjacent a surface of said slice, said conductor having a repetitive geometry for generating a pattern of attracting and repelling magnetic fields for said domains in a manner for moving single wall domains therealong from input to output positions when alternating positive and negative signals are applied thereto and means for applying said positive and negative signals to said conductor.

2. A magnetic domain propagation circuit in accordance with claim 1 in which said conductor has an asymmetric geometry for effecting domain displacement with respect thereto in the absence of applied signals.

3. A magnetic domain propagation circuit in accordance with claim 1 in which said conductor has a symmetrical geometry and means asymmetrically disposed with respect to said conductor for offsetting domains with respect to said conductor in the absence of applied signals.

4. A magnetic domain propagation circuit in accordance with claim 3 wherein said means comprises permalloy dots on the surface of said slice of material.

5. A magnetic domain propagation circuit in accordance with claim 3 wherein said means comprises recessions in said slice of material.

6. A domain propagation circuit in accordance with claim 1 wherein said slice is characterized by a preferred direction of magnetization out of the plane thereof.

7. A domain propagation circuit in accordance with claim 6 also including means for selectively generating single wall domains and means for detecting single wall domains at said input and output positions respectively.

8. A magnetic domain propagation circuit comprising a slice of material in which single wall domains can be moved and having a nonzero coercive force, and electrical conductor adjacent a first surface of said slice, said conductor having a succession of generally V-shapedportions forming a chevronshaped geometry and being aligned along an axis between input and output positions for single wall domains, and means for generating an AC current in said conductor for displacing 

1. A magnetic domain propagation circuit comprising a slice of material in which single wall domains can be moved, an electrical conductor adjacent a surface of said slice, said conductor having a repetitive geometry for generating a pattern of attracting and repelling magnetic fields for said domains in a manner for moving single wall domains therealong from input to output positions when alternating positive and negative signals are applied thereto and means for applying said positive and negative signals to said conductor.
 2. A magnetic domain propagation circuit in accordance with claim 1 in which said conductor has an asymmetric geometry for effecting domain displacement with respect thereto in the absence of applied signals.
 3. A magnetic domain propagation circuit in accordance with claim 1 in which said conductor has a symmetrical geometry and means asymmetrically disposed with respect to said conductor for offsetting domains with respect to said conductor in the absence of applied signals.
 4. A magnetic domain propagation circuit in accordance with claim 3 wherein said means comprises permalloy dots on the surface of said slice of material.
 5. A magnetic domain propagation circuit in accordance with claim 3 wherein said means comprises recessions in said slice of material.
 6. A domain propagation circuit in accordAnce with claim 1 wherein said slice is characterized by a preferred direction of magnetization out of the plane thereof.
 7. A domain propagation circuit in accordance with claim 6 also including means for selectively generating single wall domains and means for detecting single wall domains at said input and output positions respectively.
 8. A magnetic domain propagation circuit comprising a slice of material in which single wall domains can be moved and having a nonzero coercive force, an electrical conductor adjacent a first surface of said slice, said conductor having a succession of generally V-shaped portions forming a chevron-shaped geometry and being aligned along an axis between input and output positions for single wall domains, and means for generating an AC current in said conductor for displacing a single wall domain along said axis from one of said V-shaped portions to another for each alternation of said current. 